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 Post subject: 10DE7 tube
PostPosted: Sep Thu 28, 2017 12:26 pm 
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While searching for a tube for a project I ran across two 10DE7 tubes I didn't know I had in my stash.

Several years ago I played around with a 6DE7 and made an amp that could drive a 1920's speaker and seeing those tubes got me to thinking about building a push pull amp with an output impedance of 4 and/or 8 ohms.

Here's the datasheet

https://frank.pocnet.net/sheets/137/6/6DE7.pdf

Any idea what power I could expect from a pair of these and what the transformer primary impedance should be along with what B+ I should use?

I'm debating whether I should use one of the 10DE7 triodes as a phase splitter and the other as a driver for the phase splitter or if I should use both as drivers one for each power triode section and use a 12AU7, 12AT7 or 12AX7 (depending on how much gain I need) as a phase splitter and first audio tube.


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 Post subject: Re: 10DE7 tube
PostPosted: Sep Thu 28, 2017 1:53 pm 
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Well, the larger section has a max plate dissipation of 7 watts, so it's good for something..;)

I'd probably start with a 250-volt plate supply, cathode bias, and a universal output transformer....or a regular transformer driving a 5-watt load rheostat.

Do you have a distortion analyzer?

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 Post subject: Re: 10DE7 tube
PostPosted: Sep Thu 28, 2017 4:05 pm 
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For what it's worth, I made a stereo preamp a couple years back using 2 10DE7s. I was using the small triode as a gain stage and the large triode as a driver with low output impedance. For filament power, I connected the 2 10DE7s and a 6X4 in series to a 25V transformer. You might look around at 12B4 amplifier projects, from what I remember, the large triode of the 6DE7 has almost identical load lines. I am using about 300V B+ for my preamp, but it has a R-C filter in the B+ line to reduce hum, and is single ended, so I don't know if that would be useful.


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 Post subject: Re: 10DE7 tube
PostPosted: Sep Thu 28, 2017 5:21 pm 
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Mark, no distortion analyzer, but I always measure distortion like this.

I will feed a tube stage a sinewave and look at it on a scope. If the sinewave on the output looks like it did on the input then I consider the stage to have 0 distortion and I will then proceed to see how much voltage I can feed to the stage before it starts to distort to see if the output is high enough for what I need.

Not the best way to do it, but all the amps I've built using that method have sounded good. I mostly build amps for communications receivers that have low audio output power and rarely do anything HI-FI.


classicelectronicsguy, that does help a lot.

The preamp is a nifty idea.

One thing I thought of is building an amp using one tube and a resistor for the power triode plate circuit then cap coupling to an output jack so that I have something which I can connect to any audio generator and get a high voltage signal which could be used to test things like some amplifiers that require a high driving voltage.

Ran into that very issue recently when I needed to test the full output power of a push pull 45 amp which originally consisted of a driver transformer, the 45 tubes and an output tube. Had nothing that could produce enough voltage.

That said I do like the idea of a push pull amp more as that will give me another push pull triode amplifier I can use for if I get another communications receiver with a puny audio output stage.



I could get designs worked up for both and build them when needed.


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 Post subject: Re: 10DE7 tube
PostPosted: Sep Thu 28, 2017 5:32 pm 
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Measuring distortion: Set up your scope for A-B vertical display. One channel to your audio generator, and the other to the output. Tweak the gain to minimize the fundamental (any phasing difference will make thing messier, but you'll still be able to do qualitative observations.)

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 Post subject: Re: 10DE7 tube
PostPosted: Sep Thu 28, 2017 5:54 pm 
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Oh ok so basically set the two channels in subtract mode and set the gain so that there is 0 waveform showing on the scope.

Any distortion will manifest itself as a waveform of some sort, right?


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 Post subject: Re: 10DE7 tube
PostPosted: Sep Thu 28, 2017 6:53 pm 
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Exactly....

The only issue is the phasing of input and output....thus the fundamental won't completely null out. But at maybe 400Hz, it might not be an issue.

I haven't dinked around with audio for over 50 years, so apply salt as needed.....;)

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 Post subject: Re: 10DE7 tube
PostPosted: Sep Thu 28, 2017 6:55 pm 
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6DE7/10DE7/13DE7 are similar to 6DN7 and 6EA7. The gains are different but close and there are pages online for both of these tubes. You would mix the two because the triodes are not paired the same as the 6DE7 but you can get good starting points for each triode. The gain of the smaller triode is a little low like a 12AU7 or 12BH7 but not too low. I would probably use a 12AX7 front end and run the stages without cathode bypass capacitors running them at a lower gain but because of local feedback better distortion figures. You might even run the output stages this way if max output power is not your goal. Running the outputs with fixed bias and grounded cathode will give max output. If you want to ge the best noise figure you can run the 12AX7 in starved mode. This was done back in the day by many manufacturers of high fidelity preamp stages. It involves placing a resistor in series with the heater to the tube to run it cooler. Works well and will drive the grids of the 6DE7 small triodes as drivers. for a 12AX7 most of the times I saw it or used it the 12AX7 was wired for 6.3V and powered from 6.3V with a series resistor of 4.7 ohms and were always at least 1 watt but 2 watt is better and were wire wound not carbon composition.


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 Post subject: Re: 10DE7 tube
PostPosted: Sep Thu 28, 2017 7:05 pm 
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Suppose that I could get a 10Vac transformer and just run the 12AX7 with the heaters in series on 10Vac.

I would most likely go without cathode bypass caps as I'm pretty sure that I can produce more than enough voltage to drive the power triodes to full output.


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 Post subject: Re: 10DE7 tube
PostPosted: Sep Sat 30, 2017 1:23 am 
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A couple years ago used the remains of a Magnavox single ended stereo amp to build a PP 6DE7 mono version... I used one section of the orig 12AX7 preamp to drive the 6DE7s, as already mentioned the amp section of those ain't nuthing to get excited about... Using a external P/S of 250v(my B&K 1602), it'll thump pretty good... Sorry no schematic...

I also butchered up a 1955 Silvertone AA6 table radio and installed PP triode output, this one has been my daily player for almost two years...

Recently it developed a worsening hum that was caused by the 11CY7... Of the three NOS tubes I had on hand, only the one in radio didn't hum from day one(all test fine with no leakage)... Not having a humless 11CY7, I stuck a 13DR7 in it and so far it's been fine... I tried a 13DE7 but inverter gain is so low radio played about same as if the tube was removed... No doubt could have adj gain but that means pulling chassis, nope...

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 Post subject: Re: 10DE7 tube
PostPosted: Sep Sat 30, 2017 2:12 am 
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Very nice.

For now I'm just getting ideas as I don't really need another amp at the moment nor do I have the cash to build one.

I'll work up some sort of schematic and post it here.

Gonna be the power triodes being driven by the other triode in each tube with a 12AX7, 12AT7 or 12AU7 as a first audio tube and phase splitter.

I'm going to try and design the amp with HI-FI use in mind and build it that way at first which may mean I use a pentode as the first audio tube to eliminate Miller capacitance and use a single triode as a phase splitter.

That said I need to check my stash and see if I have a tube with both a pentode and triode.


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 Post subject: Re: 10DE7 tube
PostPosted: Nov Fri 03, 2017 12:21 am 
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I was pokin' around in the bell tower(garage attic) and ran across my 6DE7 PP amp...Had forgotten how good it sounds for a piece of cobbled together junk... Uses a 1950s Merit universal OPT and mostly patterned after the 11FY7 audio output in my TV tube radio, maybe I'll go ahead and draw the schematic...

Amp used to be single ended 6BQ5 Stereo but bad output transformers, and fact I needed a power xformer elsewhere led to it's demise... Control at left was a balance adj now repurposed for volume and one in center front is the adj for inverter gain... Preamp is currently one section of a 12AT7 but I'll probably l'll change the plate load resistor back to 220K for a 12AX7 or 5751...

Running on a B&K 1602 P/S with 200v B+, current draw 60ma...

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 Post subject: Re: 10DE7 tube
PostPosted: Nov Fri 03, 2017 1:52 am 
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Very nice.


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 Post subject: Re: 10DE7 tube
PostPosted: Nov Fri 03, 2017 4:16 pm 
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Tube Radio wrote:
Very nice.

LOL, had your eyes checked lately???

If I built a front panel, cleaned the chassis and revamped all the wiring, it could be fairly decent but still not "Fair" material... Mostly it's "project" chassis these days, though I kind of hate thought of butchering the 6DE7 amp... Got another picture somewhere(different computer I think) with 6BL7s... Yeah that was a trick as those are octal based...

Here it is, had a copy on this box... The 6BL7 on chassis is in the original rectifier socket while the other is "remotely" mounted... The tube sections were in parallel, Philco Amp laying on side is driving it... That amp had out of phase R&L channels plus a PP center bass channel... The R speaker connections were connected out of phase, so in reality became in phase...

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Last edited by 35Z5 on Nov Fri 03, 2017 4:50 pm, edited 1 time in total.

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 Post subject: Re: 10DE7 tube
PostPosted: Nov Fri 03, 2017 4:45 pm 
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If you've seen some of my amps they don't look very pretty either, but get the job done.

Would love to see the schematic.

I might wind up building one, but if I do I may see if I can get a transformer made with a heater winding that has 6.3, 10 and 13 volt taps on it so that I can use the 6DE7, 10DE7 or 13DE7.


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 Post subject: Re: 10DE7 tube
PostPosted: Nov Sat 04, 2017 1:04 am 
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Well I'll get'a round to drawing the schematic... Hopefully finish it in next few days...

It would be easy enough to use a pair of 10DE7 in series with a 6CG7, 6SN7 etc as preamp... That'd total to a little over 25v and those xformers are easy to find... Now you just need a B+ supply...


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 Post subject: Re: 10DE7 tube
PostPosted: Nov Sat 04, 2017 5:09 am 
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Those tubes would work as a preamp for sure.

No big rush on the schematic as it's something I may file away until I need another amplifier.


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 Post subject: Re: 10DE7 tube
PostPosted: Nov Sun 05, 2017 12:47 am 
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At moment I'm thinking it could double as a Jim Dandy plate modulator for mini xmitter... Curious if there is a marked difference in frequency response... Of course without a on board P/S, not really practical...


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 Post subject: Re: 10DE7 tube
PostPosted: Nov Sun 05, 2017 2:11 am 
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Perhaps it could.


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 Post subject: Re: 10DE7 tube
PostPosted: Nov Wed 08, 2017 6:56 pm 
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35Z5 wrote:
At moment I'm thinking it could double as a Jim Dandy plate modulator for mini xmitter... Curious if there is a marked difference in frequency response... Of course without a on board P/S, not really practical...

It does make a nice plate modulator, currently I'm driving a 6BF5 using a 6BQ5 OPT... Of course as in prior experience the transmitter is finicky and not very forgiving if bias and RF drive aren't spot on....


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